Answer:
Option 1: Restore your computer to factory settings.
A good way is to restore your computer back to its factory settings or reinstall the operating system of your computer. Of course then you will lose everything in it.

Option 2: Reset the password by using Windows Password Breaker.
This will cost you a few dollars, but it is very effective. You can reset the forgotten administrator password in Windows 7 in minutes without any data loss through this method.

Windows Password Breaker is a powerful Windows 7 password reset tool which works well on Windows 7/Vista/XP/2000 and Server 2003(R2)/2008(R2). With the help of Windows Password Breaker, you can create a bootable password reset CD/DVD or USB flash drive to reset your forgotten Windows passwords, such as Windows Local Administrator, Standard and Guest user passwords, and Windows Domain Administrator password as well.

To get started, please take steps below:
Step 1: Download and install Windows Password Breaker Professional
Step 2: Burn a bootable password reset CD/DVD or USB flash drive as the instruction
Step 3: Reboot locked computer from the burned CD/DVD/USB
Step 4: Reset lost Windows 7 administrator password

Option 3: Retrieve forgotten Windows 7 password
Ophcrack is a free Windows password cracker based on rainbow tables. It is a very efficient implementation of rainbow tables done by the inventors of the method. It comes with a Graphical User Interface and runs on multiple platforms.
This method is free of charge, but its success rate is not guaranteed and the time to get back the password is unknown.

Tip:
Living in a world that is full of various passwords, it's very easy for one to forget his password(s). For this, you'd better write down the passwords somewhere that is safe and private. When it comes to Windows 7, you can simply create a password reset disk in advance to in case of this similar problem.
Windows 7 incorporates features to create a password reset disk for its user passwords. After you reset forgotten Windows 7 password, you can create a password reset disk as follows:
1. Log into the administrator account.
2. Go to Start button, Control Panel, Family Safety and User Accounts, User Accounts.
3. Click the Create a password reset disk link on the left pane.
4. On the coming wizard, click Next.
5. Follow the wizard instructions to create that password reset disk.

Note:
1. Please label and store the password reset disk in a safe place since anyone can use this disk to change your Windows password and access your computer data.
2. This password reset disk can only be used to reset password for the user account that it's created for.